In vitro LHRH release: correlation with the LH surge and alteration by a mammary carcinogen.

The releasability of LHRH from neurosecretory terminals, as assessed in vitro by depolarization of hypothalamic synaptosomes with elevated K+, varies as a function of the time of day in parallel with the LH surge. Pretreatment of ovariectomized female rats with dimethylbenz(a)anthracene (DMBA) results in a blockade of the estrogen-induced LH surge and a blunting of LHRH release as measured in vitro. An examination of the LHRH release process revealed that K+-stimulated release of particulate LHRH was inhibited by DMBA pretreatment while basal release of particulate LHRH and both basal and K+-stimulated release of soluble LHRH were not altered. These results suggest that release of particulate LHRH is closely coupled with the estrogen-induced LH surge.